title: Slow programmable and ultra-rapid freezing of human embryos.
abstract: OBJECTIVE
  To compare the outcomes of slow freezing with ultra-rapid freezing (URF) of cleavage-stage human embryos on aluminum foil.
  
  
  METHODS
  Two-cell mouse embryos were used to test our method of ultra-rapid freezing. The embryos were randomly allocated to a non-frozen control (208 embryos), and slow (204 embryos) or ultra-rapid freezing groups (204 embryos). Immediate survival rate, further cleavage and blastocyst formation were compared. After validating our ultra-rapid freezing method on mouse embryos, we applied a similar ultra-rapid freezing protocol to human embryos. Consecutive human frozen/thawed embryo transfer (FET) cycles from October 1998 to June 2005 were reviewed. The survival rate, further cleavage rate and the pregnancy outcomes were compared between the URF and slow programmable freezing.
  
  
  RESULTS
  Mouse embryos in the URF group survived the freezing/thawing process better than those in the slow freezing group (93.1% vs 82.8%, P = 0.001). Blastocyst and hatching blastocyst formation of the surviving embryos were comparable in the URF and slow freezing group (59% vs 58.6%, P = 0.944 and 32.6% vs 42%, P = 0.066, respectively). There were 146 human FET cycles in the URF group and 28 cycles in the slow freezing group. The immediate survival of embryos was higher in the URF group than in the slow freezing group (87.9% and 64.3%, P < 0.001). There was no significant difference in the mean number of embryos per transfer (3.7 +/- 1.3 and 3.3 +/- 1.2, P = 0.178), clinical pregnancy rate per transfer (28.5% and 21.4%, P = 0.444) and implantation rate per embryo (10.98% and 10.9%, P = 0.974) in the URF or slow freezing groups.
  
  
  CONCLUSIONS
  Our in-house URF method gave comparable results to slow programmable freezing. Although the risk of potential contamination is a major drawback of the present ultra-rapid freezing technique, future refinement will minimize or entirely eliminate this concern.
authors.affiliation: Division of Reproductive Medicine, Department of Obstetrics and Gynecology, Faculty of Medicine, Chiang Mai University, Chiang Ma, Thailand. tvutyava@mail.med.cmu.ac.th
authors.forename: Teraporn
authors.initials: T
authors.lastname: Vutyavanich
authors.forename: Opas
authors.initials: O
authors.lastname: Sreshthaputra
authors.forename: Suchada
authors.initials: S
authors.lastname: Mongkolchaipak
authors.forename: Supreeya
authors.initials: S
authors.lastname: Wongtra-ngan
authors.forename: Waraporn
authors.initials: W
authors.lastname: Piromlertamorn
mesh_terms: D000818:Animals; D015925:Cryopreservation / Q000379:methods* / Q000592:standards; D004624:Embryo Transfer; D004622:Embryo, Mammalian; D047108:Embryonic Development; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D011247:Pregnancy; D011897:Random Allocation; D027724:Reproductive Techniques, Assisted